In a copending application of Norman L. Stauffer, Ser. No. 912,688, filed June 5, 1978, now U.S. Pat. No. 4,185,191, issued Jan. 22, 1980, a range determination system is shown which is useable in a through-the-lens camera for positioning the taking lens at a desired correct focus position with respect to a remote object within the field of view. That system utilizes a plurality of small detectors such as charge coupled devices (CCD) or charge injection devices (CID) mounted in an array to receive radiation from the scene being viewed. The detectors are arranged in pairs with each pair being mounted behind a small lenslet so that each pair receives a view of the exit pupil of the taking lens but one of the detectors in each pair receives radiation primarily from a first portion of the taking lens while the other of the detectors in each pair receives radiation primarily from a different portion of the taking lens. The result is to create two similar curves indicative of the radiation distribution pattern from the scene being viewed. At a proper focus position, the two curves coincide but as the object changes position with respect to the camera, the two curves move with respect to each other to indicate an out-of-focus situation. The two curves move with respect to each other in a first direction when the object is closer to the camera than the desired focus position and move in an opposite direction with respect to each other as the object moves further from the camera than the desired focus position. By determining the direction of movement of the two curves with respect to each other, it is therefore possible to determine the direction that the taking lens has to be moved to achieve the desired focus position. The system disclosed in the above-mentioned copending application determines this direction but in cameras requiring highly accurate focusing, some errors may result because there is no way to detect focus errors between adjacent detector pairs. In other words, when a proper focus position lies between adjacent detector pairs, the system may stop short of the true focus position due to receiving a first direction indication when the patterns are on one side and an opposite direction indication when the patterns are on the other side. If, for example, the lenslets are spaced 0.2 millimeters apart and a 50 millimeter focal length f2 lens is used, this may result in a focus error of over 1 millimeter at the image plane which is acceptable for many applications but not for highly accurate focusing.